A fan confused about the function of Diablo 3 Magic Find asked about the maximum possible value and got a detailed reply.
Starting in patch 1.0.8 however, the Magic Find bonus from shrines will be able to exceed the “soft cap” of 300% that players can achieve from a combination of their own gear and their follower’s gear. In patch 1.0.8 we’re also adding a buff to multiplayer games called “Strength in Numbers” which allows for a 10% bonus to Magic Find, Gold Find, and experience per additional player in a multiplayer game, up to a maximum of 30% in a four-player game. The Magic Find and Gold find bonuses of this multiplayer feature can exceed their respective 300% cap as well.
So after patch 1.0.8, if you have 300% Magic Find from your gear, have 5 stacks of NV (+75% MF), are playing on Inferno at MP10 (+250% MF), have a Fortune Shrine buff active (+25% MF), AND are playing a four player multiplayer game (+30% MF), you can hit the maximum of a 680% bonus to Magic Find. Shiny!
Keep in mind that this cap will be lower for if you aren’t playing on Inferno and/or aren’t using Monster Power level 10, etc.
At that level you should get a legendary item from approximately every 4th boss pack. If you do not, it’s because you said mean things about Jay Wilson and/or Bashiok, and Battle.net remembers.
Battle.net never forgets.